Nanoscale ordering phenomena in transition metal oxides

今天使用的大多数电子设备，如计算机和移动电话，都是基于硅芯片技术，并包含了多年来一直可用的简单金属和磁性材料。这些组件的性能已经达到极限，人们的兴趣正在转向更新的材料，作为下一代电子设备的一种方式，比如高速处理器和高密度信息存储。一类非常有前途的材料是过渡金属氧化物化合物。最近发现，其中一些化合物在纳米尺度上表现出不寻常的有序行为。电子不是均匀分布的，而是经常被发现组织成规则的模式，这不仅涉及电子的位置，还涉及它们自旋的方向和电子轨道的形状。当这些有序状态形成时，材料的可测量特性（如电阻）通常会发生突然变化，此外，这种有序通常对外部刺激（如磁场和温度）很敏感。正是这种现象的小尺度（纳米级）和可控性使这些材料在新技术中非常有前途。直到最近，人们还很难确定这些新型秩序的性质。由于x射线和中子技术的新发展，这现在成为可能。我们的研究将利用这些发展来解开这些复杂有序态的各种组成部分，并确定是什么驱动电子形成它们。我们的最终目标是了解这些状态形成的原因以及它如何影响材料的性质。这种理解对于开发新的电子应用程序是必不可少的。我们将研究一些具体的问题，它们分为两类：(1)电荷顺序与非常规超导性之间的关系；(2)与电子轨道有序相关的现象。这项工作将涉及制备和研究大量过渡金属化合物的高质量晶体，特别是铜、镍、锰和钴。我们将进行x射线和中子散射实验，以获得这些系统微观行为的窗口，我们还将进行电、磁和热力学测量，以研究排序如何影响材料的实际性能。

Most electronic equipment in use today, such as computers and mobile phones, is based on silicon chip technology, and contains simple metals and magnetic materials that have been available for many years. The performance of these components is reaching its limit, and interest is turning to newer materials as a way towards the next generation of electronic devices, such as high speed processors and high density information staorage. A very promising class of materials for this purpose is the transition metal oxide compounds. It has recently been found that some of these compounds exhibit unusual ordering behaviour on a nanometre length scale. The electrons, instead of being uniformly distributed, are often found to organise themselves into regular patterns which involve not only the positions of the electrons, but also the direction of their spin and the shape of the electron orbitals. When these ordered states form there are often abrupt changes in the measureable properties of the material, such as the resistance, and furthermore, the ordering is often sensitive to external stimuli, such as magnetic field and temperature. It is the small scale of the phenomena (nanometres) and the controllability that make these materials very promising for new technologies.Until recently it has been very difficult to determine the nature of these novel types of order. This is now becoming possible thanks to new developments in X-ray and neutron techniques. Our research will exploit these developments to unravel the various components of these complex ordered states, and to determine what drives the electrons to form them. Our ultimate goal is to understand why these states form and how it affects the properties of the material. This understanding will be essential for the development of new electronic applications.We will study a number of specific problems which fall into two categories: (1) the relationship between charge order and unconventional superconductivity, and (2) phenomena associated with ordering of the electronic orbitals. The work will involve the preparation and investigation of very high quality crystals of a large number of transition metal compounds, especially copper, nickel, manganese and cobalt. We will perform X-ray and neutron scattering experiments to gain a window on the microscopic behaviour of these systems, and we will also perform electrical, magnetic and thermodynamic measurements to study how the ordering affects the practical properties of the material.